This Austin Air pre-filter is typically included in the HEPA replacement pack, which is replaced approximately every 5 years. However, you may choose to replace the pre-filter more frequently. The pre-filter captures large particles such as dust, hair, pet dander and other visible particles, and it protects the life of Austin Air’s HEPA filter and other filters. This pre-filter is on the exterior of the filter pack and is closest to the grille. It can be vacuumed from the outside to help maintain it. Since it is on the exterior, it may also get dirtier and may lead you to want to replace it sooner than 5 years.